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Molecules 2014, 19(4), 4418-4432; doi:10.3390/molecules19044418

Synthesis of Regiospecifically Fluorinated Conjugated Dienamides

, ,  and *
Department of Chemistry, The City College and The City University of New York, 160 Convent Avenue, NY 10031, USA
* Author to whom correspondence should be addressed.
Received: 16 February 2014 / Revised: 22 March 2014 / Accepted: 31 March 2014 / Published: 10 April 2014
(This article belongs to the Special Issue Fluorine Chemistry)
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Modular synthesis of regiospecifically fluorinated 2,4-diene Weinreb amides, with defined stereochemistry at both double bonds, was achieved via two sequential Julia-Kocienski olefinations. In the first step, a Z-a-fluorovinyl Weinreb amide unit with a benzothiazolylsulfanyl substituent at the allylic position was assembled. This was achieved via condensation of two primary building blocks, namely 2-(benzo[d]thiazol-2-ylsulfonyl)-2-fluoro-N-methoxy-N-methylacetamide (a Julia-Kocienski olefination reagent) and 2-(benzo[d]thiazol-2-ylthio)acetaldehyde (a bifunctional building block). This condensation was highly Z-selective and proceeded in a good 76% yield. Oxidation of benzothiazolylsulfanyl moiety furnished a second-generation Julia-Kocienski olefination reagent, which was used for the introduction of the second olefinic linkage via DBU-mediated condensations with aldehydes, to give (2Z,4E/Z)-dienamides in 50%–74% yield. Although olefinations were 4Z-selective, (2Z,4E/Z)-2-fluoro-2,4-dienamides could be readily isomerized to the corresponding 5-substituted (2Z,4E)-2-fluoro-N-methoxy-N-methylpenta-2,4-dienamides in the presence of catalytic iodine.
Keywords: fluoro dienamides; Julia-Kocienski olefination; Weinreb amide; fluoro dienes fluoro dienamides; Julia-Kocienski olefination; Weinreb amide; fluoro dienes
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Chowdhury, M.; Mandal, S.K.; Banerjee, S.; Zajc, B. Synthesis of Regiospecifically Fluorinated Conjugated Dienamides. Molecules 2014, 19, 4418-4432.

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